As modern wireless communication systems continue to increase in popularity, a particular communications node must provide services to an ever-increasing group of subscribers. For example, in a wireless terrestrial cellular communications system, a cellular base station must maintain a capability to provide connectivity with an increasing number of users within communications range of the station. In a satellite cellular communications system, the satellite communications node must be capable of transmitting messages to, and receiving messages from, a large number of terrestrial based subscribers.
When a communications node, such as a cellular base station or a communications satellite, transmits to a group of subscribers, a single power amplifier circuit can be used to transmit the signals to the subscribers. Thus, the power amplifier circuit used to perform this transmission can be optimized for performance at a relatively high power output. However, when the power amplifier circuit is transmitting to only a single subscriber or to a small group of subscribers, the efficiency of the power amplifier circuit begins to degrade as the amplifier power output decreases. The capability for a power amplifier circuit to maintain efficiency over a wide range of power output levels is referred to as dynamic backoff range. Loss of power amplifier efficiency under dynamic backoff conditions can be especially problematic when the communications node is an orbiting satellite, where power resources are scarce and comparatively expensive.
Therefore, it is highly desirable to employ a power amplifier circuit that incorporates high efficiency techniques which can provide efficient operation over a wide dynamic backoff range. A power amplifier circuit which provides these features can reduce the primary power requirements of a satellite communications node, thereby reducing the cost of service to subscribers. this, in turn, can result in increased availability of satellite communication services to subscribers.